When the heart goes into a state of fibrillation its muscles contract in a random manner so that it cannot pump blood, but it can often be made to resume normal synchronous operation by passing a pulse of current through it. This is done by a defibrillator that discharges a storage capacitor through paddle electrodes that are pressed against certain locations on the patient's chest. As each discharge may do some damage to the heart, it is desirable to known when it has resumed normal operation. For this reason cardiographic signals are derived either from the paddle electrodes or a set of ECG electrodes and applied to form a cardiographic waveform on an oscilloscope or other display device. If the signals for the oscillocope are being derived from the paddle electrodes, it takes approximately five seconds after discharge for the voltage between them to return to zero. For most of this time the voltage is more than enough to drive the baseline for the electron beam of the oscilloscope off scale so that no waveforms can be seen. If the signals are derived from ECG electrodes of poor quality the same thing occurs. Between about one and one-half and three seconds after the discharge of the defibrillator, the heart may exhibit a few transitory beats and then revert to a condition of fibrillation. This generally means that further defibrillation discharges may be futile and that other methods such as the injection of chemicals are required in order to revive the patient. Under the condition described where no waveform appears on the oscilloscope for nearly five seconds, these transitory heart beats cannot be observed so that additional pulses of current are passed through the heart by the defibrillator. By the time it is realized that chemical methods must be used, it may well be too late.